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I am working on a wordpress site, and started implanting a CRUD database. I coded out an example that works perfectly on my localhost. However, I am working with file mangaer in cpanel, and am having difficulty with changing the regular database query to a one that is incorporated with $wpdb. I have tried to use $wpdb->get_results(), but I get the same error. Any help would be greatly appreciated.

Here is my code:

  // CONNECTION TO DATABASE
    $query = "SELECT * FROM students";
    $query_results = mysqli_query($wpdb->dbh, $query) or die(mysqli_error($wpdb->dbh));

    if(mysqli_num_rows($query_results) > 0) 
    {
        foreach($query_run as $student)
        {
            ?>
            echo '
                <form id="saveStudent">
                    <tr>' 
                        echo '<td>'<?php $student->id; ?> echo '</td>';
                        echo '<td>'<?php $student->first_name; ?> echo '</td>';
                        echo '<td>'<?php $student->last_name; ?> echo '</td>';
                        echo '<button type="button" class="btn btn-danger">Delete Student</button>'

            echo '</tr>';
            
            <?php
        }
    }
    ?>

EDIT: The error message I get is Warning: mysqli_query() expects parameter 1 to be mysqli, null given

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  • Where is this file? Is it someplace inside a theme or plugin where other WordPress functions are working?
    – WebElaine
    Oct 17, 2022 at 21:10
  • I am working within the cart page, under the web hook woocommerce_before_cart. The file itself is included in the functions.php file which is apart of cpanel's file manager
    – John Lyons
    Oct 17, 2022 at 21:14
  • Have you declared global $wpdb; before trying to use the global $wpdb object?
    – Pat J
    Oct 18, 2022 at 2:08

1 Answer 1

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Use the global $wpdb object to query your tables. The get_results() method will return your results as you need:

global $wpdb;

$query = 'SELECT * FROM students';
$query_results = $wpdb->get_results($query);
foreach ($query_results as $student) {
    // ...
}
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  • When I tried that out, I got Fatal error: Uncaught Error: Call to a member function get_results() on null
    – John Lyons
    Oct 18, 2022 at 13:59
  • @JohnLyons check your spelling $wpdb and ensure you are calling this from a WordPress or WooCommerce hook so that the global variable has been defined.
    – webaware
    Oct 18, 2022 at 22:59
  • e.g. add_action('woocommerce_before_cart', function() : void { ... });
    – webaware
    Oct 18, 2022 at 23:00

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